User manual

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14 LED light sensor
In this experiment, we are going to use a yellow LED as a
light sensor. It is installed the other way round unlike we
usual do and in consequence, it actually does not conduct
electricity. But a small current flows as soon as light falls on
the LED, very similar to a photodiode. This is then amplified
by the two transistors and will cause the other two LEDs to
light up. Try this with a flashlight. The more you illuminate
the yellow LED, the brighter the two other LEDs will glow.
Photodiode
Each diode consists of a semiconductor with a P-N junc-
tion. Current will flow readily in one direction but not in
the other, where current is blocked from flowing through.